Trichoderma-based biostimulants are considered the most effective plant growth–promoting fungi. The purpose of this study is to determine the effect of two Trichoderma saturnisporum isolates on the growth promotion of melon (Cucumis melo) seeds and seedlings as well as their effect on the performance of the cantaloupe “Charentais” melon crop cultivar Gandalf cultivated under a typical parral-type greenhouse. For these purposes, germination trials and two experiments were performed in a commercial nursery, conventional system, and large plant system. Two experiments were also established for 2 years (two crop cycles) in a commercial greenhouse in Almería, Spain. In addition, we evaluated the influence of these isolates (T1 and T2) on the Charentais melon yield and quality. High values for seedling vigor and root length were obtained by T. saturnisporum T1 (93.50%) and T2 (93.75%) against control (62%). Trichoderma saturnisporum T1 and T2 increased the quality of plants in conventional system and large plant system and can be considered as biostimulant. Trichoderma saturnisporum treatments resulted in significantly larger crop productivity without a negative effect on the fruit quality parameters. Melon productivity increased in T. saturnisporum treatments T1 (13.99%) and T2 (16.04%), while at the same time increases the average fruit weight up to 7.71% for T2 isolate. Trichoderma saturnisporum act as biostimulants for nursing and commercial melon crops without negative effects on fruit quality. This is the first report describing T. saturnisporum as a potential crop yield promoter.
Pollination is one problem with intensive seedless watermelon (Citrullus lanatus Thunb.) production under unfavorable environmental conditions (low solar radiation and temperature) due to the lowered activity of pollinating insects, such as the bee (Apis mellifera L.). An alternative to overcome these problems is the use of plant growth regulators. For this reason, experiments were conducted for 2 years in plastic greenhouses in the fields of Almeria, southwestern Spain, to evaluate the production and quality of ‘Reina de corazones’ triploid watermelon grafted onto RS841 rootstock (Cucurbita maxima × Cucurbita moschata). Two phytoregulators were used for the development of the ovary: 1-(2-chloro-4-pyridyl)-3-phenylurea (CPPU) and 2,4-dichlorophenoxyacetic acid (2,4-D). Concentrations of CPPU evaluated were 50, 100, 150, and 200 mg·L−1. An application of 0.6 mL was applied to each ovary in addition to 4, 6, 8, or 12 mg·L−1 of 2,4-D to the foliar mass at a proportion of 1000 L·ha−1. Results showed that the production and number of fruit obtained with CPPU treatments were similar to what is obtained by using bees for fruit pollination. Maximum production was reached at concentrations of 100–200 mg·L−1. Average production was 32% to 83% higher than results from 2,4-D at 8 mg·L−1. The number of fruit per plant was 33% to 35% higher as well. In the first assay, a positive correlation was also observed between production and CPPU concentration. CPPU treatments had a lower accumulation of sugars than those with 2,4-D; nevertheless, both treatments showed values of commercially acceptable soluble solids.
The silicon (Si) percentage in the dry matter of plants is between 0.1% and 10%, and even though its role in the metabolism of plants is not absolutely clear, Si’s positive effects on plant nutrition and plant protection against both biotic and abiotic stress are well documented. However, Si is not considered to be an essential element, so it is not always present in nutrient solutions. In this paper, an experiment was carried out in the University of Almeria’s greenhouse with hydroponic lettuce, tomato, pepper, melon, and cucumber plants. A standard nutrient solution was used as a control sample and was fertigated with Si. During the four-true-leaf seedling stage, various plant growth parameters were measured, including the dry weight and the wet weight as well as the foliar surface and the cuticle thickness of both the leaf and the stem. Additionally, in the lettuce, tomato, and pepper plants, the effect of the use of Si in the nutrient solution on the protection against the pathogen Botrytis cinerea was determined by measuring the penetration of the pathogen through the cuticle and the extension of the fungal infection by using leaf discs. The results suggest that all of the studied parameters, and both the cuticle thickness and the epidermis thickness, were increased by more than 10% on average for all of the plants. In the lettuce, tomato, and pepper plants, a beneficial effect against B. cinerea was observed when the nutrient solution containing Si was used.
In Spain, the adoption of the triploide ‘Queen of Hearts’ (Citrullus lanatus Thunb.) watermelon cultivar has brought important changes in the production of seedless watermelon thanks to its magnificent acceptance by the market. The experiments on triploid watermelon presented here examined innovative production techniques that would guarantee the productivity and quality of this cultivar in plastic greenhouses and improve cost-effectiveness, serving growers. Crop intensification was tested under a “temporary trellis” management system, increasing plant density from 2500 plants/ha in the traditional or creeping crop system to 10,000 plants/ha. The “temporary trellis” system was combined with fruit set through the localized application of a 150- to 200-mg·L−1 solution of 1-(2-chloro-4-pyridyl)-3-phenylurea (CPPU). The increase of grafted watermelon plant density to 1 plant/m2 gave rise to an increase in early harvest measured as the number of fruits per surface area compared with the traditional system with a density of 0.25 plant/m2. In addition, a process of temporary trellising facilitates choosing female flowers for applying CPPU. The °Brix and pulp firmness quality parameters did not show significant differences between “temporary trellised” and creeping crops.